Polysilicon structure including protective layer

ABSTRACT

A semiconductor device includes a substrate, a first polysilicon structure over a first portion of the substrate, and a first spacer on a sidewall of the first polysilicon structure. The first spacer has a concave corner region between an upper portion and a lower portion. The semiconductor device includes a second polysilicon structure over a second portion of the substrate. The semiconductor device includes a second spacer on a sidewall of the second polysilicon structure. The semiconductor device further includes a protective layer covering an entirety of the first spacer and the first polysilicon structure, wherein the protective layer has a first thickness over the concave corner region and a second thickness over the first polysilicon structure, a difference between the first thickness and the second thickness is at most 10% of the second thickness, and the protective layer exposes a top-most portion of a sidewall of the second spacer.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No.16/101,784 filed Aug. 13, 2018, which is a divisional of U.S.application Ser. No. 14/158,239, filed Jan. 17, 2014, now U.S. Pat. No.10,050,035, issued Aug. 14, 2018, which are incorporated herein byreference in their entireties.

BACKGROUND

In some applications, a logic circuit, static random access memory(SRAM), and one-time-programmable (OTP) memory of an integrated circuitare fabricated on the same substrate. In some applications, whenperforming a self-aligned silicide (salicide) process to form electricalcontacts on the logic or SRAM part, the OTP part of the integratedcircuit is protected by a protective layer. The performance of the logiccircuit, the SRAM, and the OTP memory is affected by the thickness ofthe protective layer in the OTP part and residue of materials used toform the protective layer in the SRAM part.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of an integrated circuit in accordancewith some embodiments.

FIG. 2 is a flow chart of a method of fabricating an integrated circuitin accordance with some embodiments.

FIGS. 3A to 3C are cross-sectional views of an integrated circuit atvarious manufacturing stages in accordance with some embodiments.

FIG. 4 is a cross-sectional view of an integrated circuit that isfabricated by a process different from that depicted in FIG. 2 inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

By forming a layer of protective material that is sufficiently thick andyet conformal to a contour of a polysilicon structure and correspondingspacers of an integrated circuit, a process window of a subsequentremoval process is enlarged compared to a non-conformal layer ofprotective material. As a result, the integrated circuit has a bettersilicide formation in the logic or SRAM part and better leakageprevention in the OTP part. In some embodiments, the disclosedembodiments are suitable to be used in a Bipolar-CMOS-DMOS (BCD)process. Bipolar stands for bipolar junction transistors, CMOS standsfor complementary metal-oxide-semiconductor transistors, and DMOS standsfor double-diffused metal-oxide-semiconductor transistors.

FIG. 1 is a cross-sectional view of an integrated circuit 100 inaccordance with some embodiments. In some embodiments, integratedcircuit 100 depicted in FIG. 1 is an intermediate product, which will befurther processed by one or more manufacturing processes in order toform a functional integrated circuit. Other active electrical componentsand passive electrical components of the integrated circuit 100 are notshown in FIG. 1 .

Integrated circuit 100 has a substrate 110, a first polysiliconstructure 122, a second polysilicon structure 124, a first set ofspacers 132, a second set of spacers 134, and a protective layer 142.

In some embodiments, substrate 110 includes: an elementary semiconductorsuch as silicon or germanium in crystal, polycrystalline, or anamorphous structure; a compound semiconductor including silicon carbide,gallium arsenide, gallium phosphide, gallium nitride, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; orcombinations thereof. In at least one embodiment, substrate 110 is analloy semiconductor substrate having a gradient SiGe feature in whichthe Si and Ge composition change from one ratio at one location toanother ratio at another location of the gradient SiGe feature. Inanother embodiment, the alloy SiGe is formed over a silicon substrate.In yet another embodiment, a SiGe substrate is strained. In some furtherembodiments, substrate 110 is a semiconductor on insulator. In someexamples, substrate 110 includes an epitaxial layer or a buried layer.In other examples, substrate 110 includes a multilayer compoundsemiconductor structure.

In some embodiments, substrate 110 generally exhibits a conductivecharacteristic similar to that of an intrinsic semiconductor material ora semiconductor material having a predetermined doping type. In someembodiments, the predetermined doping type is a P-type doping.

Substrate 110 has a first portion 112 and a second portion 114. In someembodiments, two or more of a logic circuit, a static random accessmemory (SRAM), or a one-time-programmable (OTP) memory are fabricated onsubstrate 110, where the OTP memory is formed on first portion 112 ofsubstrate 110, and the logic circuit and/or the SRAM are formed onsecond portion 114 of substrate 110. In some embodiments, the logiccircuits, SRAM, and OTP memory are fabricated using a bipolar-CMOS-DMOS(BCD) process. In other words, in some embodiments, at least one bipolarjunction transistor (BJT) device, at least one complementarymetal-oxide-semiconductor (CMOS) device, and at least onedouble-diffused metal-oxide-semiconductor (DMOS) device are formed onsubstrate 110.

First polysilicon structure 122 is over first portion 112 of substrate110. First set of spacers 132 includes two spacers on opposite sidewallsof first polysilicon structure 122. Spacers 132 are L-shaped spacers. Insome embodiments, spacers 132 have a shape other than an L-shape. Insome embodiments, spacers 132 have a material including silicon nitride.In some embodiments, spacers 132 have a multi-layer structure. In someembodiments, integrated circuit 100 has a one-time-programmable (OTP)device that includes first polysilicon structure 122 and spacers 132. Insome embodiments, a gate dielectric (not shown) is formed betweenpolysilicon structure 122 and substrate 110. In some embodiments, one ormore layers of other materials are formed between polysilicon structure122 and substrate 110.

Second polysilicon structure 124 is over second portion 114 of substrate110. Second set of spacers 134 includes two spacers on oppositesidewalls of second polysilicon structure 124. Spacers 134 are L-shapedspacers. In some embodiments, spacers 134 have a shape other than anL-shape. In some embodiments, spacers 134 have a material includingsilicon nitride. In some embodiments, spacers 134 have a multi-layerstructure. In some embodiments, integrated circuit 100 has a logiccircuit or an SRAM that includes second polysilicon structure 124 andspacers 134. In some embodiments, a gate dielectric (not shown) isformed between polysilicon structure 124 and substrate 110. In someembodiments, one or more layers of other materials are formed betweenpolysilicon structure 124 and substrate 110.

In some embodiments, first and second polysilicon structure 122 and 124are concurrently formed and include similar materials. In someembodiments, first and second set of spacers 132 and 134 areconcurrently formed and include similar configuration and materials.

Protective layer 142 covers first portion 112 of substrate 110, firstpolysilicon structure 122, and first set of spacers 132. Protectivelayer 142 is free from covering second portion 114 of substrate 110,second polysilicon structure 124, and second set of spacers 134. Athickness of protective layer 142 is measureable as a distance betweenan upper surface 142 a and a lower surface 142 b of protective layer 142along a normal direction of the lower surface 142 b of protective layer142. Protective layer 142 having a thickness H₁ over first polysiliconstructure 122, and the thickness H₁ is equal to or greater than 500 Å.In some embodiments, thickness H₁ represents the maximum thickness ofprotective layer 142 directly over first polysilicon structure 122.Protective layer 142 having a thickness H₂ over spacers 132, and thethickness H₂ is equal to or less than 110% of the first thickness H₁. Insome embodiments, thickness H₂ represents the maximum thickness ofprotective layer 142 directly over spacers 132. In some embodiments, themaximum thickness of protective layer 142 over spacers 132 occurs atabout a corner portion 132 a of the spacers 132.

Protective layer 142 thus provides sufficient protection to firstpolysilicon structure 122 while second polysilicon structure 124 isbeing processed by a silicide process. Also, the difference betweenthickness H₂ and thickness H₁ is small enough (equal to or less than 10%of thickness H₁) that eases a requirement for the processing window fora subsequent protective layer removal process.

FIG. 2 is a flow chart of a method 200 of fabricating an integratedcircuit 100 in accordance with some embodiments. FIGS. 3A to 3C arecross-sectional views of integrated circuit 100 at various manufacturingstages in accordance with some embodiments. Components in FIGS. 2 and 3Ato 3C that are the same or similar to those in FIG. 1 are given the samereference numbers, and detailed description thereof is omitted. It isunderstood that additional operations may be performed before, during,and/or after the method 200 depicted in FIG. 2 , and that some otherprocesses may only be briefly described herein.

As depicted in FIG. 2 and FIG. 1 , the process 200 begins at operation210, where first polysilicon structure 122 is formed over first portion112 of substrate 110 and second polysilicon structure 124 is formed oversecond portion 114 of substrate 110. In some embodiments, operation 210includes forming a layer of polysilicon material over substrate 110 andthen patterning the layer of polysilicon material into first and secondpolysilicon structures 122 and 124 by performing a lithographic processfollowed by a removal process.

The process 200 proceeds to operation 220, where first set of spacers132 and second set of spacers 134 are formed on sidewalls of polysiliconstructure 122 and 124. In some embodiments, operation 220 includesforming a layer of spacer material over first and second polysiliconstructures 122 and 124 and substrate 110 and then patterning the layerof spacer material into first and second sets of spacers 132 and 134 byperforming a removal process. In some embodiments, the layer of spacermaterial includes silicon nitride. In some embodiments, the removalprocess includes an anisotropic etch process.

FIG. 3A is a cross-sectional view of integrated circuit 100 afteroperation 220.

As depicted in FIG. 2 and FIG. 1 , the process 200 proceeds to operation230, where one or more other electrical components are also formed onsubstrate 110. In some embodiments, integrated circuit 100 is fabricatedby a BCD process, and operation 230, in conjunction with operations 210and/or 220, are usable to form at least one bipolar junction transistor(BJT), at least one complementary metal-oxide-semiconductor (CMOS)device, and at least one double-diffused metal-oxide-semiconductor(DMOS) device on substrate 110. In some embodiments, operation 230 isperformed before, after, or concurrently with operations 210 and 220. Insome embodiments, operation 230 is omitted.

The process 200 proceeds to operation 240, where a layer of protectivematerial is formed over substrate 110. In some embodiments, the layer ofprotective material includes silicon oxide, and operation 240 includesperforming an ozone-tetraethyl orthosilicate (TEOS) high aspect ratioprocess (HARP) or an atomic layer deposition (ALD) process. In someembodiments, the ozone-TEOS HARP process or the ALD process is suable toform a layer of protective material that is conformal to a contour ofpolysilicon structure 122 and 124 and corresponding spacers 132 and 134of an integrated circuit 100, even when the thickness of the layer ofprotective material over polysilicon structure 122 and 124 is equal toor greater than 500 Å.

FIG. 3B is a cross-sectional view of integrated circuit 100 afteroperation 240. A layer of protective material 140 covers the first andsecond polysilicon structures 122 and 132 and first and second sets ofspacers 132 and 134.

The layer of protective material 140 has a thickness H₁ over firstpolysilicon structure 122, and the thickness H₁ is equal to or greaterthan 500 Å. In some embodiments, thickness H₁ represents the maximumthickness of the layer of protective material 140 over first polysiliconstructure 122. The layer of protective material 140 having a thicknessH₂ over spacers 132, and the thickness H₂ is equal to or less than 110%of the first thickness H₁. In some embodiments, thickness H₂ representsthe maximum thickness of the layer of protective material 140 overspacers 132.

Also, the layer of protective material 140 has a maximum thickness H₃over second polysilicon structure 124, and the maximum thickness H₃ isequal to or greater than 500 Å. The layer of protective material 140having a maximum thickness H₄ over spacers 134, and the thickness H₄ isequal to or less than 110% of the thickness H₃. In some embodiments, thedifference between thickness H₄ and thickness H₃ is small enough (e.g.,equal to or less than 10% of thickness H₃) that eases a requirement forthe processing window for one or more subsequent protective layerremoval processes.

As depicted in FIG. 2 and FIG. 1 , the process 200 proceeds to operation250, where a patterned photo resist layer is formed over a portion ofthe layer of protective material 140 and the first portion of substrate112.

FIG. 3C is a cross-sectional view of integrated circuit 100 afteroperation 250. A patterned photo resist layer 310 is formed to cover afirst portion 142 of the layer of protective material 140 that coversthe first portion 112 of the substrate 110 and to expose a secondportion 144 of the layer of protective material 140 that covers thesecond portion 114 of the substrate 110.

As depicted in FIG. 2 , FIG. 1 , and FIG. 3C, the process 200 proceedsto operation 260, where the second portion 144 of the layer ofprotective material 140 is removed. In some embodiments, operation 260includes performing a dry etch process or a wet etch process, or acombination thereof. In some embodiments, operation 260 includesperforming a dry etch process and then performing a wet etch processafter the performing the dry etch process. After operation 260,patterned photo resist layer 310 is removed by an ashing process.

Because the layer of protective material 140 is conformally formed alonga contour of polysilicon structure 124 and spacers 134, the processwindow for the dry etch process is sufficient large for yield control,and the process window for the wet etch process is sufficient large forprotective layer peeling prevention.

FIG. 1 depicts a cross-sectional view of integrated circuit 100 afteroperation 260.

As depicted in FIG. 2 , the process 200 proceeds to operation 270, wherea self-aligned silicide (salicide) process is performed on the secondportion 114 of the substrate 110 while the first portion 112 of thesubstrate 110 is covered by the first portion 142 of the layer ofprotective material. The process 200 then proceeds to operation 280,where a logic circuit or an SRAM cell is formed based on the secondpolysilicon structure 124 and spacers 134, and an OTP device is formedbased on first polysilicon structure 122 and spacers 132. In someembodiments, operation 280 is omitted, and polysilicon structures 122and 124 are used to form other types of electrical components.

FIG. 4 is a cross-sectional view of an integrated circuit 400 that isfabricated by a process different from that depicted in FIG. 2 inaccordance with some embodiments. Components in FIG. 4 that are the sameor similar to those in FIG. 1 are given the same reference numbers, anddetailed description thereof is omitted.

Integrated circuit 400 includes a protective layer 412 over firstpolysilicon structure 122, first set of spacers 132, and first portion112 of substrate 110. Integrated circuit 400 further includes residueprotective materials 414 near the corner portion 134 a of second set ofspacers 134 of and extending to an upper surface of second portion 114of substrate 110.

Compared with integrated circuit 100, a processing operation comparableto operation 240 for manufacturing integrated circuit 400 is performedby a Plasma-enhanced chemical vapor deposition (PECVD) process. ThePECVD process causes accumulation of protective materials at cornerportions 132 a and 134 a. As a result, when a thickness H₅ of protectivelayer 412 over first polysilicon structure 122 is equal to or greaterthan 500 Å, a thickness H₆ of protective layer 412 around corner portion132 a of first set of spacers 132 is greater than 110% of thickness H₅.In some embodiments, thickness H₆ of protective layer 412 is greaterthan 120% of thickness H₅.

At a stage comparable to FIG. 3C, second polysilicon structure 122 ofintegrated circuit 400 is covered by a layer of protective material in amanner similar to protective layer 412 over first silicon structure 122.The difference between thickness H₆ and thickness H₅ is too large(greater than 10% of thickness H₅) that renders a requirement for theprocessing window for a subsequent protective layer removal process morestringent than that of operation 260 or technically infeasible. As aresult, residue protective materials 414 near the corner portion 134 aof second set of spacers 134 are not fully removed.

In some embodiments, residue protective materials 414 hinder asubsequent salicidation process comparable to operation 270. In someembodiments, in order to reduce or eliminate residue protectivematerials 414, protective layer 412 becomes too thin to effectivelyprotect polysilicon structure 122 from the subsequent salicidationprocess intended for polysilicon structure 124 and/or second portion ofsubstrate 114.

An aspect of this description relates to a semiconductor device. Thesemiconductor device includes a substrate and a first polysiliconstructure over a first portion of the substrate. The semiconductordevice further includes a first spacer on a sidewall of the firstpolysilicon structure, wherein the first spacer has a concave cornerregion between an upper portion and a lower portion. The semiconductordevice further includes a second polysilicon structure over a secondportion of the substrate. The semiconductor device further includes asecond spacer on a sidewall of the second polysilicon structure. Thesemiconductor device further includes a protective layer covering anentirety of the first spacer and the first polysilicon structure,wherein the protective layer has a first thickness over the concavecorner region and a second thickness over the first polysiliconstructure, a difference between the first thickness and the secondthickness is at most 10% of the second thickness, and the protectivelayer exposes a top-most portion of a sidewall of the second spacer. Insome embodiments, the protective layer covers a curved portion of thesecond spacer. In some embodiments, the thickness of the protectivelayer over the first polysilicon structure is at least 500 angstroms. Insome embodiments, the protection layer over the first spacer isconformal to the first spacer. In some embodiments, at least one of thefirst spacer or the second spacer is a multi-layer structure. In someembodiments, a material of the first spacer is a same material as thesecond spacer.

An aspect of this description relates to a manufacture. The manufactureincludes a substrate and a polysilicon structure over a portion of thesubstrate. The manufacture further includes two spacers on oppositesidewalls of the second polysilicon structure, wherein each spacer ofthe two spacers has a concave corner region between an upper portion anda lower portion. The manufacture further includes a protective layerexposing the portion of the substrate, the polysilicon structure, andpartially exposing the two spacers above the concave corner region, andthe protective layer covers an entirety of the lower portion of the twospacers. In some embodiments, a width of the lower portion is greaterthan a width of the upper portion. In some embodiments, a top-mostsurface of the polysilicon structure is coplanar with a top-most surfaceof each of the two spacers. In some embodiments, the protective layercovers an entirety of the concave corner region of the two spacers. Insome embodiments, each of the two spacers is a multi-layer structure. Insome embodiments, a material of each of the two spacers is differentfrom a material of the protective layer. In some embodiments, theprotective layer covers a section of the upper portion adjacent to theconcave corner region.

An aspect of this description relates to a semiconductor device. Thesemiconductor device includes a substrate and a first polysiliconstructure over a first portion of the substrate. The semiconductordevice further includes a first spacer on a sidewall of the firstpolysilicon structure, wherein the first spacer has a first concavecorner region between an upper portion and a lower portion. Thesemiconductor device further includes a second polysilicon structureover a second portion of the substrate. The semiconductor device furtherincludes a second spacer on a sidewall of the second polysiliconstructure, wherein the second spacer has a second concave corner region.The semiconductor device further includes a first protective layercovering an entirety of the first spacer and the first polysiliconstructure, wherein the first protective layer comprises a firstmaterial. The semiconductor device further includes a second protectivelayer over the second concave corner region, wherein the secondprotective layer exposes a top-most portion of a sidewall of the secondspacer, and the second protective layer comprises the first material. Insome embodiments, the first protective layer has a first thickness overthe first concave corner region and a second thickness over the firstpolysilicon structure, and the first thickness is different from thesecond thickness. In some embodiments, a difference between the firstthickness and the second thickness is at most 10% of the secondthickness. In some embodiments, the first thickness is greater than thesecond thickness. In some embodiments, the second protective layercovers an entirety of the second spacer below the second concave cornerregion. In some embodiments, a portion of the substrate between thefirst polysilicon structure and the second polysilicon structure is freeof both the first protective layer and the second protective layer. Insome embodiments, a width of the lower portion is greater than a widthof the upper portion.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a substrate;a first polysilicon structure over a first portion of the substrate; afirst spacer on a sidewall of the first polysilicon structure, whereinthe first spacer has a concave corner region between an upper portionand a lower portion; a second polysilicon structure over a secondportion of the substrate; a second spacer on a sidewall of the secondpolysilicon structure; and a protective layer covering an entirety ofthe first spacer and the first polysilicon structure, wherein theprotective layer has a first thickness over the concave corner regionand a second thickness over the first polysilicon structure, adifference between the first thickness and the second thickness is atmost 10% of the second thickness, and the protective layer exposes atop-most portion of a sidewall of the second spacer.
 2. Thesemiconductor device of claim 1, wherein the protective layer covers acurved portion of the second spacer.
 3. The semiconductor device ofclaim 1, wherein the thickness of the protective layer over the firstpolysilicon structure is at least 500 angstroms.
 4. The semiconductordevice of claim 1, wherein the protection layer over the first spacer isconformal to the first spacer.
 5. The semiconductor device of claim 1,wherein at least one of the first spacer or the second spacer is amulti-layer structure.
 6. The semiconductor device of claim 1, wherein amaterial of the first spacer is a same material as the second spacer. 7.A manufacture, comprising: a substrate; a polysilicon structure over aportion of the substrate; two spacers on opposite sidewalls of thepolysilicon structure, wherein each spacer of the two spacers has aconcave corner region between an upper portion and a lower portion, eachspacer of the two spacers has an outer sidewall and an inner sidewall,and the inner sidewall is between the outer sidewall and the polysiliconstructure; and a protective layer exposing the portion of the substrate,the polysilicon structure, and exposing a portion of the outer sidewallof each of the two spacers above the concave corner region, and theprotective layer covers an entirety of the lower portion of the twospacers.
 8. The manufacture of claim 7, wherein a width of the lowerportion is greater than a width of the upper portion.
 9. The manufactureof claim 7, wherein a top-most surface of the polysilicon structure iscoplanar with a top-most surface of each of the two spacers.
 10. Themanufacture of claim 7, wherein the protective layer covers an entiretyof the concave corner region of the two spacers.
 11. The manufacture ofclaim 7, wherein each of the two spacers is a multi-layer structure. 12.The manufacture of claim 7, wherein a material of each of the twospacers is different from a material of the protective layer.
 13. Themanufacture of claim 7, wherein the protective layer covers a section ofthe upper portion adjacent to the concave corner region.
 14. Asemiconductor device, comprising: a substrate; a first polysiliconstructure over a first portion of the substrate; a first spacer on asidewall of the first polysilicon structure, wherein the first spacerhas a first concave corner region between an upper portion and a lowerportion; a second polysilicon structure over a second portion of thesubstrate; a second spacer on a sidewall of the second polysiliconstructure, wherein the second spacer has a second concave corner region,the second spacer has an inner sidewall and an outer sidewall, and theinner sidewall is between the outer sidewall and the second polysiliconstructure; a first protective layer covering an entirety of the firstspacer and the first polysilicon structure, wherein the first protectivelayer comprises a first material; and a second protective layer over thesecond concave corner region, wherein the second protective layerexposes a top-most portion of the outer sidewall of the second spacer,and the second protective layer comprises the first material.
 15. Themanufacture of claim 14, wherein the first protective layer has a firstthickness over the first concave corner region and a second thicknessover the first polysilicon structure, and the first thickness isdifferent from the second thickness.
 16. The manufacture of claim 15,wherein a difference between the first thickness and the secondthickness is at most 10% of the second thickness.
 17. The manufacture ofclaim 15, wherein the first thickness is greater than the secondthickness.
 18. The manufacture of claim 14, wherein the secondprotective layer covers an entirety of the second spacer below thesecond concave corner region.
 19. The manufacture of claim 14, wherein aportion of the substrate between the first polysilicon structure and thesecond polysilicon structure is free of both the first protective layerand the second protective layer.
 20. The manufacture of claim 14,wherein a width of the lower portion is greater than a width of theupper portion.